This invention relates to apparatus for extracting liquid from a suspension and more particularly to sludge filtering apparatus wherein free water or water which is easily removed is extracted from the solid materials to thus partially de-water the suspension whereby the suspension is thickened prior to delivery to conventional filter apparatus for further removal of liquid.
Heretofore in the art to which my invention relates, various devices have been proposed for partially de-watering suspensions, such as sludge. For example, perforated conveyor belts for filtering purposes have been employed. Such filtering conveyors have also been combined with complicated filter press installation wherein the suspension is confined between spaced apart perforated conveyor belts and pressure is applied by means of rollers. Also, the efficiency of such perforated conveyor belts has been improved by supplementing the gravity effect and the roller pressure effect with a vacuum which is applied to the liquid discharge side of the perforated conveyor belt. Such apparatus not only increases the energy consumption but also greatly increases the belt's friction. Problems have been encountered with such perforated conveyor belts due to the fact that they become plugged with solid materials which cannot be satisfactorily extracted, even with the application of vacuum beneath the belt.
Prior attempts to counteract the plugging of the perforated conveyor belts have included scraping elements which remove the deposited solid matter from the belt's surface in order to allow the liquid to reach the perforations in the belt. Such a device is disclosed in U.S. Pat. No. 2,097,529. Also, U.S. Pat. No. 3,984,329 discloses a filtering device wherein sludge is deposited as a sludge bed on a substantially horizontal conveyor belt. As the sludge moves along, it encounters a series of laterally and longitudianally spaced flow breakers which are subjected to an angular biasing force which urges them into a normal operating position against the movement of the sludge bed on the conveyor. Such apparatus is not only complicated and expensive but it requires a considerable amount of maintenance for satisfactory operation thereof.